PLEASANTON -- A bicyclist suffered major injuries while on a ride with his son-in-law in the Pleasanton Ridge Regional Park on Saturday, a fire department official said.

Around 9:35 a.m., fire crews responded to reports of a bicyclist down at an unknown location inside the park, according to Battalion Chief Joe Testa of the Livermore-Pleasanton Fire Department.

The fire department sent two off-road vehicles to initiate a search for the man, who has not been identified, from both the Augustine Bernal Park access via the Golden Eagle Trail and the Foothill Road staging area. After 30 minutes, the man was found on the Thermalito Trail on the west side of the ridge, suffering from serious injuries, Testa said.

The man was flown via a medical helicopter to Eden Medical Center. His condition has not been released.

Testa said the man's son in-law assisted rescuers in locating the man and providing information as to what led to the incident.

No other cyclists were involved in the crash.

It is not known why the man veered off the bike path.

Contact Katie Nelson at knelson@bayareanewsgroup.com or follow her at Twitter.com/katienelson210.